Elementary Graph-Set Descriptors in Crystal Structure Comparison of 2‑Methyl-4-Nitroanilinium Hexachloridostannate(IV), Bromide and Two Noncentrosymmertic Chlorides. X‑Ray, Vibrational and Theoretical Studies

Crystal structures of two polymorphs of [H2m4na]Cl (1α,1β) and (H2m4na)2SnCl6·H2O (2), where 2m4na = 2-methyl-4-nitroaniline are shown and comparison of these crystal structures with the bromide salt reported earlier is presented. In all the presented crystal structures, alternatively arranged cations and anions form chain and ring hydrogen-bonding patterns of weak unconventional N–H···Cl hydrogen bonds. Interrelations among the elementary graph-set descriptors and descriptors of the hydrogen-bonding patterns are presented. Nonhydrogen bonding interactions between the nitro groups are also described using graph-set descriptors. Comparison of the experimental, also for deuterated 1α polymorph, and theoretical, for H2m4na+ ion with B3LYP/6-31G­(d,p), spectra showed good agreement among the frequencies due to very weak interactions existing in studied compounds. Detailed analysis of the spectra revealed that the interaction between adjacent −NO2 groups in 1α is stronger than the other types involving the nitro group. The bands were assigned on the basis of theoretical calculations of vibrational frequencies for H2m4na+ ion and PED analysis.